The invention relates to the technical sector of the production of plasma by electron cyclotron resonance (ECR) from a gas medium.
More particularly, the invention relates to the vacuum plasma surface treatment of any type of filiform components such as wires, tubes, fibres and more generally any other product the length of which is very long with respect to the diameter. The filiform component being continuously linearly driven.
Vacuum surface treatment by plasma refers to cleaning, pickling, activation, grafting of functions of coating of the surface for example by PECVD (Plasma-Enhanced Chemical Vapour Deposition) of the filiform component.
Many technical solutions to perform microwave applicators for the treatment of different types of parts are known. One can cite as an example, for information and without limitation purposes, the teaching of the patent EP 1075168 which relates to a process and a device to produce elementary plasmas in a view of creating an uniform plasma for a surface of use. One can also cite the teaching of the patent FR 2 922 358 which relates to a surface treatment process of at least one part by means of elementary plasma sources by electron cyclotron resonance. The different solutions resulting from these patents are particularly suited to the treatment of large surfaces or batches of parts placed next to one another and generally with multiple faces to be treated.
According to the prior art by using a microwave applicator with magnetic end piece, it appears that the plasma is generated at the end of each magnet creating a dense area of plasma. It is also known that in order to generate a low pressure microwave plasma, the electron cyclotron resonance effect is used. The probability of high speed shocks is considerably increased which creates a dense plasma in the ECR area. Thus, for a frequency of 2.45 GHz, the ECR area is at the magnetic field lines at 875 Gauss (G). This area at 875 Gauss (G) is around the magnet.
This technology of plasma application is not suitable for the continuous treatment of a wire (or other filiform component) requiring several applicators placed radially and repeated several times according to the running axis of the wire to be treatment to obtain a running speed.
Indeed, the volume of plasma being punctually located at the end of the applicators, several applicators all around the wire (or other filiform component) must be used to guarantee an axisymmetrical uniform deposition. Such a configuration requires a large deposition chamber which consumes large quantities of gas and energy. The multiplication of the applicators and the lack of compactness make this system expensive to build.
It therefore appears that the juxtaposition of conventional ECR sources does not allow obtaining a plasma configuration favourable to deposition on a filiform component.
For the treatment of wires under vacuum, according to the state of the art, PVD (physical vapour deposition) type treatments were proposed as made apparent from the teaching of the documents WO 2005/095078, WO 2006/002673, FR 2667616 and EP 1231292, EP 1277874.
U.S. Pat. No. 6,638,569 is also known according to which a conventional vacuum chamber is used and the wire is subjected to multiple reciprocating movements in the chamber in order to expose the maximum of surface of the wire to the plasma. This solution is of little efficiency as the surface of the wire is negligible with respect to the size of the chamber and results in relative complexity by implementing vacuum operating return systems.
From this state of the art, the aim sought is to be able to perform a surface treatment under vacuum by plasma as previously described on any type of filiform component. According to the teaching of U.S. Pat. No. 5,595,793, a coating is deposited by PECVD, for example a carbon coating, on a fibre by using a surface plasma microwave to generate the plasma. However, this solution is very limited in application given that it can only operate on dielectrics and only to perform electrical insulating depositions. In other words, conductive fibres cannot be coated. Furthermore, the frequency of the generator should be adapted to the dielectric constant of each material constituting the fibre. The process is therefore not easily transferable by switching from one material to another. Finally the process is difficult to control because as and when the deposition is executed, the dielectric constant of the material changes. This change has a retroactive effect on the coupling of the surface wave with the plasma.
It is therefore made apparent from this analysis of the state of the art that the plasma generation using applicators, is not suitable for the continuous treatment of filiform components, as the volume of the chamber is oversized with respect to the size of the component, the precursor gas and the energy required is significant whereas the plasma is not generated close to the wire to be coated. It is also made apparent that the alternative microwave plasma techniques based on surface waves are limited in their applications and difficult to implement.
The invention is aimed at overcoming these disadvantages in a safe, efficient and rational manner.
The problem the invention proposes to overcome is to allow for the generation of a linear plasma confined around any type of filiform component as defined, in order to minimise the volume of the chamber, and, consequently, the investment in the consumption of precursor gas and energy required in the aim of generating axisymmetrical plasma in order to guarantee the homogeneity of the treatment on the part, in particular by PECVD.